Organic carbon availability limiting microbial denitrification in the deep vadose zone.

Microbes in the deep vadose zone play an essential role in the mitigation of nitrate leaching; however, limited information is available on the mechanisms of microbial denitrification due to sampling difficulties. We experimentally studied the factors that affect denitrification in soils collected down to 10.5 meters deep along the soil profile. After an anoxic pre-incubation, denitrification rates moderately increased and the N2 O/(N2 O + N2 ) ratios declined while the microbial abundance and diversity did not change significantly in most of the layers. Denitrification rate was significantly enhanced and the abundance of the denitrification genes was simultaneously elevated by the increased availability of organic carbon in all studied layers, to a greater extent in the subsurface layers than in the surface layers, suggesting the severe scarcity of carbon in the deep vadose zone. The genera Pseudomonas and Bacillus, which are made up of a number of species that have been previously identified as denitrifiers in soil, were the major taxa that respond to carbon addition. Overall, our results suggested that the limited denitrification in the deep vadose zone is not because of the lack of denitrifiers, but due to the low abundance of denitrifiers which is caused by low carbon availability.

[Assessment of humic and fulvic acids in black soils using near-infrared reflectance spectroscopy].

The organic carbon content and optical densities of humic acids in black soils of China were predicted and assessed using near infrared spectroscopy technique. The contents of humic acid (HA) and fulvic acid (FA) in 136 black soil samples in China were analyzed and the NIR spectra were collected using a VECTOR/22 (Fourier transform infrared spectroscopy). Partial least squares (PLS) regression with cross validation was used to develop prediction models with reference data and soil NIRS spectra, and the model was validated using an independent set of samples. NIRS well predicted (HAC+FAC), HAC and FAC contents, with R2 = 0.92, 0.92 and 0.86, RPD = 3.66, 3.82 and 2.69, and high correlation coefficients between predicted and measured values (r = 0.90, 0.85 and 0.82). Predictions for the E4 values of HA and FA were also good (R2 = 0.85, 0.85; RPD = 2.88, 2.65; r = 0.92, 0.80). Predictions for optical densities of HA and FA at 665 nm (E6) was acceptable. Generally, NIRS showed a good potential to predict C content and optical densities of humic acid and fulvic acid in blacks soils and may reveal information on SOC quality.

[Prediction of soil organic carbon in different soil fractions of black soils in Northeast China using near-infrared reflectance spectroscopy].

The soil organic carbon (SOC) associated with different soil fractions varies in the composition and dynamics. The present work is aimed to evaluate the potential of near infrared spectroscopy (NIRS) to predict SOC content in different soil fractions of black soils. SOC contents of 136 black soil samples in China were analyzed and the NIR spectra were collected using a VECTOR/22 (Fourier transform infrared spectroscopy). Partial least squares (PLS) regression with cross validation was used to develop calibrations between reference data and NIRS spectra (n = 100) which were validated using an independent set of samples (n = 36). Predictions for water-sieved aggregate associated organic carbon were generally good with R2 (coefficient of determination) ranging from 0.69 to 0.82 and the RPD (residual prediction deviation) from 1.2 to 1.8. NIRS well predicted the SOC in < 53 microm mineral fraction (R2 = 0.97, RPD = 5.4), but the prediction for SOC in 250-2 000 microm or in 53-250 microm particulate matter fractions was poor. However, the prediction for the SOC in 53-2 000 microm fraction was good (R2 = 0.79, RPD = 2.2). In addition, NIRS very well predicted the SOC in fine particle fraction (< 20 microm) (R2 = 0.93, RPD = 3.8). Accordingly, NIRS showed a good potential to predict SOC in some soil fractions and could reduce tedious laboratory analysis.

[Research progress on soil aggregates and associated organic carbon in salinized soils]. / ç›æ¸åŒ–æ¡ä»¶ä¸‹åœŸå£¤å›¢èšä½“åŠå ¶æœ‰æœºç¢³ç ”ç©¶è¿›å±•.

Soil aggregate, as a basic component of soils, plays an important role in improving soil structure and enhancing soil organic carbon (SOC) sequestration. The special soil properties induced by salinization, such as high ion concentrations (mainly Na+), shortage of organic material and bad condition of microbe, inhibit the formation and stability of soil aggregate. Therefore, it is important and meaningful to explore the dynamics of aggregate in salinized soils. Coastal wetland and inland salinized marsh wetland are important salinized ecosystems. We systematically summarized the progress and achievements on soil aggregate in salinized agriculture and wetland ecosystems. Agricultural practices, such as organic and/or inorganic soil amendment application, tillage practice, vegetation type, straw return and saline water irrigation, advance the formation and stability of aggregate and aggregate-associated organic carbon in salinized soils. We discussed the problems and deficiency in the present studies of aggregate and aggregate-associated carbon in salinized soils as well as the research aspects and hot topics in the future. This review would be helpful for comprehensively understanding the advances and development directions on aggregate in salinized soils.

Effects of different Tamarix chinensis-grass patterns on the soil quality of coastal saline soil in the Yellow River Delta, China.

Construction of circumlittoral shelter forest is of great significance to maintain ecological security of coastal zones, the safety of people's lives and property in the Yellow River Delta (YRD) in China. Tamarix chinensis-grass patterns have shown obvious advantages in construction of circumlittoral shelter forest and improving the soil quality of coastal saline soil. This study aimed to explore the soil-improving effects of various Tamarix chinensis-grass community patterns and identify the best vegetation pattern for improving the soil quality in the coastal saline-alkali land. Six kinds of Tamarix chinensis-grass community patterns were selected from the saline-alkali soil of the YRD, with bare land as the control. Effects of different Tamarix chinensis-grass patterns on the coastal saline soil were evaluated using statistical methods (e.g. principal component analysis and fuzzy membership function method). The results showed that various Tamarix chinensis-grass community patterns significantly decreased the salt contents and increased the available nutrient contents in the coastal saline-alkali soil. The soil improvement effects showed obvious distinctions among the different Tamarix chinensis-grass patterns. The mixed forest-grass pattern consisting of Tamarix chinensis, Phragmites australis, and other salt-resistant grasses showed the best effects in relation to reducing salt, preventing alkalization and increasing the soil nutrients, which resulted in the lowest salt contents and the highest nutrients. Grass species play a major role in increasing soil nutrient contents, and the density of new Tamarix chinensis forest contributes greatly to the decrease of soil salt. And the more kinds of grass species are, the better improvement effects they will have. Therefore, during the construction of the circumlittoral shelter forest system in the muddy coastal zone of the YRD, it is recommended to prioritize the high density Tamarix chinensis-Phragmites australis (TPA) community pattern, and live together with other kinds of salt-resistant grasses.

Mesoporous Layered Graphene Oxide/Fe3O4/C3N3S3 Polymer Hybrids for Rapid Removal of Pb2+ and Cd2+ from Water.

Mesoporous layered magnetic hybrid GFP2 composed of C3N3S3 polymers, Fe3O4 nanoparticles (Fe3O4 NPs), and graphene oxide with a mesoporous layered "sandwich"-like structure was successfully explored by in situ simple polymerization tactic for rapid removal of Pb2+ and Cd2+ from water. It shows good selectivity and high adsorption capacity (277.78 and 49.75 mg/g) for Pb2+ and Cd2+, respectively. It exhibits the fast adsorption kinetics (>80% elimination efficiency in less than 30 min). The Langmuir isotherm model based on typical monomolecular layer adsorption fits better with the data of adsorption than the Freundlich isotherm model. The adsorption process of GFP2 for Pb2+ and Cd2+ can be explained well with the pseudo-second-order kinetics model. GFP2 is a kind of recyclable solid absorbent, which is an excellent candidate in the heavy metal wastewater treatment. More importantly, GFP2 was set with Fe3O4 NPs which makes it easily separable from wastewater with an extra magnet.

[Effects of tillage mode on black soil's penetration resistance and bulk density].

Taking an eight-year field experiment site in Dehui County of Jilin Province, Northeast China as test object, this paper studied the effects of different tillage modes (no tillage and ploughing in autumn) on the penetration resistance and bulk density of black soil. No tillage increased the soil penetration resistance, especially at the soil depth of 2.5-17.5 cm. In the continuous cropping of maize and the rotation of maize-soybean, the maximum soil penetration resistance at planting zone under no tillage and ploughing in autumn was 2816 and 1931 kPa, and 2660 and 2051 kPa, respectively, which had no restriction on the crop growth. The curve of soil penetration resistance under ploughing in autumn changed with ridge shape, while that under no tillage changed less. Comparing with ploughing in autumn, no tillage increased the bulk density of 5-20 cm soil layer significantly. Under no tillage, the bulk density of 5-30 cm soil layer changed little, but under ploughing in autumn, soil bulk density increased gradually with increasing soil depth. There was no significant correlation between soil bulk density and soil penetration resistance.